1. Field of the Invention
The present invention relates to an electrostatic type micro transducer such as a micro sensor and a micro actuator, and a control system using the same, and in particular relates to an electrostatic type micro transducer having an improved yield during the production thereof and an excellent reliability during the use thereof, and a control system using the same.
2. Description of Related Art
In general, a plurality of physical forces due to several kinds of mechanisms act between surfaces of solid bodies, in particular in a micro sensor which is constituted by micro structural bodies the ratio of their surface area with respect to their masses becomes large so that the mutual action between the surfaces plays an important role. For example, a plurality of attractive forces due to several kinds of mechanisms are induced between movable parts or between a movable part and a stationary part which are facing each other with or without a microscopic gap therebetween so that it sometimes happens that both parts stick to each other to render the micro sensor inoperative.
An example of conventional micro sensors serving as an accelerometer is disclosed in JP-A-60-244864 (1985), which corresponds to U.S. Pat. Nos. 4,574,327 and 4,609,968, wherein a plurality of dielectric stops are provided on a movable capacitor plate to prevent a short circuiting current flowing between the movable capacitor plate and an opposing fixed capacitor plate when both are contacted.
In the above conventional micro sensor, the technical problem with regard to prevention of short circuiting current between the movable and fixed capacitor plates has been resolved by means of the dielectric stops, however no consideration is given with regard to prevention of sticking by physical forces between the movable electrode plate and the stationary electrode plate in a micro sensor because of the very existence of the dielectric stops. Namely, in the micro sensor such as an electrostatic type micro sensor and an electrostatic servo type micro sensor, the movable electrode may be attracted toward the stationary electrode due to an electrostatic attraction force during the production thereof or during the handling thereof before or after mounting thereof, when a high voltage is applied for some causes between the movable electrode and the stationary electrode or when a charged external body touches the micro sensor and a static electricity is charged between the both electrodes, such is caused, for example, when clothes, charged by static electricity, of a worker touches to an electrode terminal of the micro sensor during the handling thereof. At this moment, a high electric field is applied to an electric insulator film such as the dielectric stop provided on the electrodes, thus a dielectric polarization thereof, a movement of movable electric charges such as ions contained within the insulator film, an injection of electric charges from the outside into the insulator film and an accumulation of electric charges in the interfaces between the insulator film and electrodes are caused thereby a spacial distribution of electric charges is generated inside the insulator film or at the vicinity of the interfaces between the insulator film and the electrodes, and such spacial electric charge distribution may remain even after the electric field caused from the outside is removed.
Because of these residual dielectric polarization and residual electric charges, an attractive force due to the electrostatic force is caused between the facing electrodes spaced apart with the electric insulator film and a microscopic gap. As a result, there arises an undesirable phenomenon of continuous sticking of the movable electrode and the stationary electrode via the insulator film, herein the term "sticking" is used to indicate a phenomenon wherein facing contacting surfaces connect each other by microscopic physical forces other than chemical bonding forces acting on the respective facing surfaces.